It is well known that ultrasonic sensors are used for many driver aid applications to assist vehicle drivers. In such automotive applications, ultrasonic sensors use sound waves that pass through air (i.e. a fluid medium) to determine that an object is present and to determine its distance. One driver aid application is to detect an object of concern that the driver might not be aware of when the vehicle is backing up. Another driver aid application is to assist the driver in determining that an appropriate parking spot is available when the vehicle is in Park Assist mode. These driver aid applications are accomplished by using a plurality of ultrasonic sensors to detect objects and determine distance between such object and the sensor(s). Providing required information for these and other types of driver aid applications can necessitate mounting one or more of such ultrasonic sensors in close proximity to an engine compartment of the vehicle. For example, it is becoming common for a plurality of ultrasonic sensors to be mounted on a front bumper of a vehicle in addition to the well known mounting of a plurality of ultrasonic sensors in a rear bumper of the vehicle. However, unlike placement of the ultrasonic sensors in the rear bumper, ultrasonic sensors in the front bumper are typically exposed to heat from the engine compartment.
The ability of an ultrasonic sensor to detect objects and report their distance can be adversely impacted as the temperature of the outside air (i.e., temperature of outside air surrounding the vehicle) changes and/or temperature of the sensor(s) changes. For example, some ultrasonic sensors used in automotive applications begin exhibiting diminished object detection capability as the temperature of the sensor reaches about 40-50 degrees Celsius. To assist with mitigating such temperature based variability in sensing performance of such ultrasonic sensor(s), vehicle systems typically make use of the outside air temperature data that is used to display outside temperature to vehicle users to compensate for changes in temperature as it relates to ultrasonic sensor performance. The sensor used to determine the outside air temperature data (i.e., the outside air temperature sensor) can be located in or near to an engine compartment of a vehicle. For example, the outside air temperature sensor is often located on the grill or other forward structure of a vehicle. As a result, heat from an engine of the vehicle can affect accuracy of the ambient air temperature data provided by the outside air temperature sensor, especially when vehicle is standing still. To help prevent inaccuracies in outside air temperature data arising from engine heat, algorithms are used to counteract the effects of the engine heat by restricting the raise of the displayed outside air temperature. This restriction can result in an inaccurate estimation of the sensor's actual temperature.
Accordingly, temperature compensation for ultrasonic sensors can have a significant error that is highly undesirable because temperature of ultrasonic sensors and the temperature of the medium through which they sense objects affects signal strength calibrations (e.g., echo thresholds) applied when detecting an object. In order to increase the detection capabilities and reported distance of an object, ultrasonic sensors need to adjust their detection criteria and distance calculations as the temperature of air surrounding a vehicle (i.e., outside air temperature) changes and also as the temperature of the sensor changes. Therefore, a simple, effective and consistent approach for determining a temperature upon which such detection criteria and distance calculations adjustments can be based would be beneficial, desirable and useful.